This invention relates to an intra-observation apparatus for observing the interior of the blood vessel of a human subject.
Recently, a very narrow endoscope has been developed for observing the interior of the blood vessel for the medical treatment of the arterio-sclerosis or the interior of the blood vessel subsequent to the percutaneous transluminal coronary angioplasty or the blood-vessel bypass operation. This type of endoscope is guided to a region of interest (ROI) through a guide sheath which has been inserted into the blood vessel. However, since the blood runs through the blood vessel, it is not possible to observe the state of the inner wall or valve (ROI) of the blood vessel even it is illuminated with illumination light. It is the usual practice to inject a transparent liquid, such as a physiological saline, into a gap between the guide sheath and the endoscope or into a channel provided in the endoscope so that the blood stream at the ROI is locally replaced temporarily with the injected transparent liquid for observation to be made without hindrance. In this case, in order to make continuous observation, it is necessary that the transparent liquid be continuously injected under a certain pressure level into the ROI against the blood stream. As means for injecting the transparent liquid, use is made of a manual injector to allow a transparent liquid to be manually injected into an infusion tube which has been inserted into the injection, or an automatic injector. Such a type of automatic injector is disclosed, for example, in Japanese Patent Disclosure (KOKAI) No. 59-172621, which is adapted to detect a variation in an amount of received light varying in accordance with a variation in the reflection surface of the blood vessel and to automatically control an amount of transparent liquid in accordance with the variation level.
Where the blood stream is locally to be replaced by a transparent liquid with the use of a conventional intra-observation apparatus, if a pressure level is set too low prior to the injection of the transparent liquid, the blood stream is not adequately displaced with a liquid against the blood pressure due to too small a flow of the transparent liquid involved, failing to observe the inner wall of the blood vessel. If the pressure level is set too high, on the other hand, the transparent liquid will be injected into the blood vessel to an extent exceeding a requisite level. Needless to say, it is desirable from the physiological viewpoint that the amount of transparent liquid injected into the blood vessel be as small as required. Furthermore, the amount of transparent liquid required for observation varies, depending upon the inner diameter of the blood vessel at the ROI of the human subject. In the conventional method, a trial and error operation has to be repeated in an attempt to determine an optimum amount of transparent liquid injected, making it necessary to inject an extra liquid into the blood stream.
In the aforementioned conventional apparatus, since the transparent liquid is injected into the blood stream at a fixed level of flow irrespective of the interior state of the blood vessel under observation, various troubles may be caused, from the physiological viewpoint, due to an extra flow of the transparent liquid, thus providing a greater bar to a greater acceptance of the operation using an endoscope.
In this type of apparatus as disclosed in Japanese Patent Disclosure (KOKAI) No. 59-172621, a very complex arrangement is required at the distal end of an endoscope and hence the endoscope is technically difficult to implement. Where such a complex arrangement is adopted at a very narrow endoscope of a type adapted to be inserted into the blood vessel, the insertion section of the endoscope becomes larger in its outer diameter and the resultant endoscope causes a greater burden on the patient. Furthermore, the endoscope detects pressure exerted on, or the flow velocity prevalent at, the distal end of the endoscope. Thus the apparatus cannot determine whether the liquid at the distal end of the endoscope is the blood or the transparent liquid. It is thus impossible to make continuous observation.